The present invention relates to sealing devices comprising containers and synthetic resin caps having tamper-evidence capabilities for sealing the mouth portions of these containers.
In recent years, synthetic resin containers composed of polyethylene terephthalate (PET bottles) have come into common use as beverage containers. Synthetic resin containers have the advantageous properties of being light and shatterproof in comparison to conventional glass bottles.
Additionally, as caps for this type of synthetic resin, metallic caps of aluminum alloy or the like have been conventionally used. The use of synthetic resin caps is also being advanced to replace these types of metallic caps.
With regard to these types of synthetic resin caps, those disclosed in Japanese Patent Application, First Publication No. Sho 62-251352 and Japanese Patent Application, First Publication No. Hei 2-296666 are known.
These conventional synthetic resin caps are screwed onto containers having an external thread formed on the mouth portions and annular expanded portions below the external thread; the caps are composed of a synthetic resin cap main body formed by a top plate portion and a tubular portion which extends downward from the peripheral portions thereof, and a thin liner provided on the inner surface of the top plate portion of the cap main body, the cap main body being such that the bottom portion thereof is separated, by means of a horizontal score formed around the circumference while leaving a plurality of thin bridges, into a main portion above and a tamper-evidence ring portion below the horizontal score. A threaded portion for screwing onto the external thread on the container mouth portion is formed on the inner wall surface of the main portion of the cap main body, and multiple wings or tabs are provided so as to be capable of being uplifted on the inner wall surface of the tamper-evidence ring portion.
Additionally, as the containers, those having an external thread formed on the outer circumference of the top end portion of the mouth portion and provided with an annular expanded portion (locking ring) below the external thread are used.
With these types of caps having tamper-evidence capabilities, the relationship between the rotational angle (the seal release angle, hereinafter abbreviated to SRA) at the moment the seal of the container is released due to the top end of the container mouth portion being separated from the inner surface of the cap or the liner when the cap attached to the container mouth portion is rotated from the initial position in the direction of opening, and the rotational angle (the bridge breaking angle, hereinafter abbreviated to BBA) at the position where the bridges are broken when the cap attached to the container mouth portion is rotated from the initial position in the direction of opening is held to preferably be such that SRA --BBA=0 degrees or greater, more preferably +30 degrees or greater.
However, with the above-mentioned synthetic resin caps, there are cases wherein the bridges formed from synthetic resin expand and the engaging projections (wings or tabs) are so soft as to bend when engaging with the annular expanded portion, as a result of which the BBA can increase and SRA-BBA can become less than 0 degrees; thus, there are points requiring improvement from the point of view of tamper-evidence capabilities.
As sealing devices designed to increase the above-described tamper evidence capabilities using synthetic resin caps, those described in Japanese Patent Application, Second Publication No. Hei 3-56990 are known. These sealing devices comprise engaging claws having engaging side edges extending downward with a tilt in the cap-opening direction underneath the external thread of the container, and engaged claws which cooperate with the above-mentioned container engaging claws formed on the inner walls of the tamper-evidence ring portion of the cap. With the sealing device of Japanese Patent Application, Second Publication No. Hei 3-56990, when the cap is turned in an cap-opening direction with the cap attached to the container mouth portion, the engaged claws formed on the tamper-evidence ring portion are guided to the tilted engaging side edges of the engaging claws so as to be forced downward, and the tamper-evidence ring portion is forced to move downward to accelerate tearing along the tear line formed on the cap tube portion.
However, in these conventional sealing devices, since the engaged claws formed on the cap have a fixed structure such as not to bend, the engaged claws on the cap side must be forced past the engaging claws on the container when the cap is attached to the container, so that the plurality of bridges which couple the main portion of the cap tube portion with the tamper evidence portion must be reinforced to some extent, as a result of which the resistance to breakage of the bridges when the cap is opened is large and the seal cannot be easily opened. Additionally, in order to prevent the bridges from breaking when the cap is attached (sealing), the tamper-evidence ring portion could be given an engaging structure for preventing relative movement in the cap-closing direction, but this presents a problem in that it would become difficult to mold the cap and the costs would increase. Furthermore, since these containers according to the conventional art are for engaging the engaged claws having fixed structures such as not to bend, these containers cannot be applied to caps provided with multiple wings or tabs which are capable of standing on the inner wall surface of the tamper-evidence ring portion as described in Japanese Patent Application, First Publication No. Sho 62-251352 and Japanese Patent Application, First Publication No. Hei 22-96666. That is, with the structure of the container described in Japanese Patent Application, Second Publication No. 3-56990, only engaging claws having engaging side edges extending downward while tilting in the cap-opening direction are formed underneath the external thread, so that when the cap is turned in a cap-opening direction and the wings or tabs contact the tips of the engaging claws, their tips are bent upward, allowing the engaging claws to pass without engaging the engaging claws, as a result of which the cap can be removed without breaking the bridges.
Additionally, as another example of conventional art, those described in Japanese Patent Application, First Publication No. Hei 7-291317 have been proposed.
The sealing device described in this publication comprises an external thread on the mouth portion of the container, an annular chin portion positioned therebelow, and ratchet claws positioned therebelow spaced along the circumferential direction. An internal thread is formed on the inner circumferential surface of the main portion of the tube portion of the synthetic resin cap, and engaging flaps which extend upward at an incline in the radial inward direction from the base end are formed on the inner circumferential surface of the tamper-evidence ring portion spaced in the circumferential direction.
When this type of sealing device formed by combining a container with a cap has the mouth and neck portions sealed by attaching the cap to the mouth portion of the container, the rotation of the cap, not the movement in the upward direction, is inhibited due to the tips in the circumferential direction of the engaging flaps formed on the tamper-evidence portion of the cap contacting the rear surfaces of the ratchet claws which rapidly extend at an incline.
That is, the conventional sealing device composed of a synthetic resin cap and a container as mentioned above has a format wherein, when the cap attached to the container mouth portion is turned in the cap-opening direction, the engaging flaps formed on the inner circumferential surface of the tamper-evidence ring portion of the cap are engaged with the ratchet claws formed on the container mouth portion to inhibit the rotation of the tamper-evidence ring portion in the cap-opening direction, as a result of which a force in the rotational direction is directly applied to a plurality of bridges which couple the main portion of the cap tube portion with the tamper-evidence ring portion to break the bridges.
However, with regard to the above-mentioned conventional sealing devices, since the bridges are severed by pulling apart the plurality of bridges at once, there is a risk that the rupture resistance of the bridges could increase so that the bridges are not sufficiently severed, or that the engaging flaps could be folded back due to the strong rupture resistance so as to pass the ratchet claws.
That is, in the weakened line of a cap tube portion formed from a horizontal score cut along the circumferential direction of the tube portion while leaving a plurality of thin bridges, each bridge has a thin pillar shape composed of synthetic resin. This type of bridge is comparatively easily stretched when a tensile force is applied in the longitudinal direction, and easily and reliably severs after a certain degree of stretching. However, when shear stress arising from the movement of the main portion which is turned in the cap-opening direction with respect to the fixed tamper-evidence ring portion is instantaneously applied to this type of bridge, the bridge has a high rupture resistance. In other words, tamper-evidence portions coupled to main portions by means of multiple bridges in this way are not easily torn even when a rotational force is applied in the cap-opening direction.
Additionally, with formats wherein bridges are severed according to conventional products as mentioned above, a large cap-opening torque is required in order to separate the tamper-evidence ring portion from the main portion, and this makes it difficult for children to open the cap. Additionally, even if one attempts to open the cap by applying a large cap-opening torque, this large force can be applied to the engaging flaps so as to cause the engaging flaps to be folded back and pass the ratchet claws, thereby making it impossible to separate the tamper-evidence ring portion.
The present invention has been achieved in consideration of the above-described situations, and has the object of offering a sealing device and container which prevents the cap-opening torque from becoming high due to the rupture resistance of the bridges when the cap attached to the container mouth portion is turned in the cap-opening direction, and which can yield good tamper-evidence capabilities by reducing the BBA when the cap is being opened.